Polyolefin and composition for pipe systems and sheets

ABSTRACT

A polyolefin composition for pipes comprising (percent by weight):
         A) from 1% to 9.5%; of a copolymer of propylene and hexene-1 wherein said copolymer comprises from 0.1 to 5% of recurring units derived from hexene-1;   B) from 80.5% to 99% of a heterophasic polypropylene composition comprising:   B1) from 50% to 85% of a propylene homopolymer, said propylene polymer being insoluble in xylene at ambient temperature in an amount over 85% having a polydispersity Index ranging from 3 to 10; and a Melt Index from 0.5 to 10 dg/min;   B2) from 5% to 50% of a copolymer of ethylene and propylene having an ethylene derived units content ranging from 30% to 70%;   said polymeric composition having a Melt Index from 0.05 to 10 dg/min.

This application is the U.S. national phase of International ApplicationPCT/EP2011/059424, filed Jun. 8, 2011, claiming priority to EuropeanPatent Application 10167048.7 filed Jun. 23, 2010, and the benefit under35 U.S.C. 119(e) of U.S. Provisional Application No. 61/398,366, filedJun. 24, 2010; the disclosures of International ApplicationPCT/EP2011/059424, European Patent Application 10167048.7 and U.S.Provisional Application No. 61/398,366, each as filed, are incorporatedherein by reference.

The present invention relates to a polyolefin composition suitable toproduce pipe systems and sheets.

Pipes, tubing and fittings are intended within the term of pipe systems.

The term sheets includes sheets for thermoforming and plates to be usedin the preparation of semi-finished products such as those employed inchemical industry.

The sheets or plates are mainly being used in the production of articlessuch as containers for housewares and food, for example juicecontainers, yogurt cups, margarine tubs and others. Said sheets orplates can also be used in the production of automotive parts.

The pipe systems according to the present invention are particularlysuitable to transport, outdoor and indoor, fluids under high pressureand/or gravity sewerage and their handling during installation is veryeasy.

In pressure pipe applications polypropylene is appreciated in hot andcold water distribution systems inside and outside buildings and/or whenhigh chemical resistance is required.

Pipes wherein the polypropylene plastic material is used in place of thecurrently used plastic materials are not usually used till now, due toan insufficient balance of mechanical properties, in particularinsufficient balance between hydraulic pressure resistance and impactresistance of the polypropylene material, especially at low temperature.

Patent application WO 2006/002778 discloses mono or multilayer pipesystems having at least one layer comprising a semi-crystallinecopolymer of propylene and hexene-1 and, optionally, a further recurringunit derived from the olefins selected from ethylene and a C₄-C₁₀α-olefin, wherein said copolymer contains from 0.2 to 5 wt %, preferably0.5 to 5 wt % of recurring units derived from hexene-1. Pipe systemsaccording to the above mentioned invention show a very high hydraulicpressure resistance which provides pipes with high durability. Thedrawback related to said systems is low impact resistance expressed bythe low values of IZOD test, particularly at low temperatures. Thisaspect is critical because this property is associated with workabilityand handling of the pipes during installation. Pipes based on materialshaving low impact resistance values become not workable and theirhandling is difficult when the temperature is lower than 10° C., that isvery common during the cold seasons in most of the countries.

Patent application WO 2005/014713 discloses a heterophasic polypropylenecomposition suitable for non-pressure pipe applications, such as wastewater pipes, for both indoor use and, preferably, outdoor use. Saidcomposition provides pipe systems with good impact properties. However,we have found that pipe systems made from said composition have very lowvalues of hydraulic pressure resistance, therefore said composition cannot be used for pipe systems transporting fluids under high pressure fora long time.

WO 2008/077773 discloses a polymeric composition comprising (percent byweight):

1) 10-60% of a copolymer of propylene and hexene-1 wherein saidcopolymer comprises from 0.2 to 10% of recurring units derived fromhexene-1, preferably from 0.5 to 8%, more preferably ranging from 1 to6%; and

2) 10-85% of a propylene polymer selected from propylene homopolymer anda polymer of propylene with 0.1-10% of a α-olefin selected fromethylene, a C₄-C₁₀ α-olefin, hexene-1 excluded, and a mixture thereof,said propylene polymer being insoluble in xylene at ambient temperaturein an amount over 85% and having a Polydispersity Index ranging from 3to 20; and

3) 5-30% of a copolymer of ethylene with a C₃-C₁₀ α-olefin andoptionally a diene, having an ethylene content ranging from 15 to 60%and an intrinsic viscosity value of at least 1 g/ml.

This document is completely silent about the possibility to lower theamount of component 1) under 10%.

The applicant found that it is possible to improve the stiffness of apolyolefin pipe systems containing 1-hexene and at the same timeincreasing the tensile stress resistance.

Thus an object of the present invention is a polyolefin compositioncomprising (percent by weight):

A) from 1.0% to 9.5%; preferably from 2.0% to 8.0%, more preferably from3.0% to 7.0% of a copolymer of propylene and 1-hexene wherein saidcopolymer comprises from 0.1 to 5.0% of recurring units derived from1-hexene, preferably from 0.3 to 3.0%, more preferably ranging from 0.3to 2.0% even more preferably from 0.4 and 1.0%; and

B) from 80.5% to 99.0% preferably from 82.0% to 98.0%, more preferablyfrom 83.0% to 97.0% of a heterophasic polypropylene compositioncomprising:

B1) from 50.0% to 85.0% preferably from 60.0% to 82.0% even morepreferably from 75.0% to 82.0% of a propylene homopolymer, saidpropylene polymer being insoluble in xylene at ambient temperature in anamount over 85.0% having a polydispersity Index ranging from 3 to 10;preferably from 4 to 8 and a Melt Index from 0.5 to 10 dg/min,preferably from 0.6 to 5 dg/min, even more preferably from 0.6 to 2dg/min according to ISO method 1133;

B2) from 5.0% to 50.0% preferably from 8.0% to 40.0% even morepreferably from 8.0% to 15.0% of a copolymer of ethylene and propylenehaving an ethylene derived units content ranging from 30.0% to 70.0%,preferably from 40.0% to 60.0%, more preferably from 45.0% to 55.0% evenmore preferably from 51.0% to 55.0%.

Said polymeric composition having a Melt Index (MFR) from 0.05 to 10dg/min, preferably from 0.1 to 3 dg/min more preferably from 0.2 to 1dg/min, according to ISO method 1133.

Said polymeric composition and the articles derived therefrom have anoptimal balance of mechanical properties; they show a Flexural Modulushigher than 1500 MPa, preferably higher than 1700 MPa.

The distribution of hexene-1 in and among the polymer chains may vary.In particular it may be that its content is higher in the polymer chainshaving high molecular weight with respect to its content in lowermolecular weight chains.

The intrinsic Viscosity was determined in tetrahydronaphthalene at 135°C.

The values of Polydispersity Index (P.I.) in component A) can range from3 to 15, preferably from 4 to 10, even more preferably from 5 to 8.

For Polydispersity Index is intended the rheological measurement of theMolecular Weight Distribution determined as described below.

The propylene-hexene-1 copolymers used in the present invention have astereoregularity of isotactic type of the propylenic sequences shown byhigh value of xylene insolubility.

Preferably the propylene-1-hexene copolymer component A) is endowed withat least one of the following features:

-   -   a melting temperature equal to or higher than 135° C.,        preferably equal to or higher than 140° C., such as from 140 to        155° C.; and    -   a solubility in xylene at ambient temperature (i.e. about 25°        C.) lower than 12 wt %, preferably lower than 9 wt % with        respect to the total weight of the propylene-hexene-1 copolymer.

The propylene-hexene-1 copolymers used in the present invention can beprepared by a polymerization in one or more polymerization steps. Suchpolymerization can be carried out in the presence of Ziegler-Nattacatalysts. An essential component of said catalysts is a solid catalystcomponent comprising a titanium compound having at least onetitanium-halogen bond, and an electron-donor compound, both supported ona magnesium halide in active form. Another essential component(co-catalyst) is an organoaluminium compound, such as an aluminium alkylcompound.

An external donor is optionally added.

The catalysts generally used for producing the propylene-hexene-1copolymers of the invention are capable to provide polypropylene with avalue of xylene insolubility at ambient temperature greater than 90%,preferably greater than 95%.

Catalysts having the above mentioned characteristics are well known inthe patent literature; particularly advantageous are the solid catalystcomponents used in the catalysts described in U.S. Pat. No. 4,399,054,European patents Nos. 45977 and 395083. The solid catalyst componentsused in said catalysts comprise, as electron-donor compounds (internalelectron-donor compounds), compounds selected from the group consistingof ethers, ketones, lactones, compounds containing N, P and/or S atoms,and esters of mono- and dicarboxylic acids. Particularly suitableelectron-donor compounds are phthalic acid esters, such as diisobutyl,dioctyl, diphenyl and benzylbutyl phthalate, and esters of succinicacids. Among phthalic acid esters the diisobutyl phthalate isparticularly preferred.

Particularly suitable internal electron donor compounds are selectedfrom succinates disclosed in international patent applicationWO00/63261.

Other electron-donors particularly suitable are 1,3-diethers describedin EP 361493 and EP 728769.

Representative examples of said diethers are as follows:2-methyl-2-isopropyl-1,3-dimethoxypropane,2,2-diisobutyl-1,3-dimethoxypropane,2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane,2-isopropyl-2-isoamyl-1,3-dimethoxypropane and 9,9-bis(methoxymethyl)fluorene.

The preparation of the above mentioned catalyst components is carriedout according to various methods. For example, a MgCl₂.nROH adduct (inparticular in the form of spherical particles) wherein n is generallyfrom 1 to 6 and ROH is ethanol, butanol or isobutanol, is reacted withan excess of TiCl₄ containing the electron-donor compound. The reactiontemperature is generally from 80 to 120° C. The solid is then isolatedand reacted once more with TiCl₄, in presence or absence of theelectron-donor compound, after which it is separated and washed withaliquots of a hydrocarbon until all chlorine ions have disappeared. Inthe solid catalyst component the titanium compound, expressed as Ti, isgenerally present in an amount from 0.5 to 10% by weight. The quantityof electron-donor compound which remains fixed on the solid catalystcomponent generally is 5 to 20% by moles with respect to the magnesiumdihalide. The titanium compounds, which can be used for the preparationof the solid catalyst component, are the halides and the halogenalcoholates of titanium. Titanium tetrachloride is the preferredcompound.

The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls,such as Altriethyl, Al-triisobutyl, Al-tributyl, and linear or cyclicAl-alkyl compounds containing two or more Al atoms bonded to each otherby way of O or N atoms, or SO₄ or SO₃ groups. The Al-alkyl compound isgenerally used in such a quantity that the Al/Ti ratio is from 1 to1000.

The electron-donor compounds that can be used as external donors includearomatic acid esters such as alkyl benzoates and in particular siliconcompounds containing at least one Si—OR bond, where R is a hydrocarbonradical. Examples of preferred silicon compounds are(tertbutyl)₂Si(OCH₃)₂, (cyclopentyl)₂Si(OCH₃)₂, (cyclohexyl)(methyl)Si(OCH₃)₂ and (isopropyl)₂Si(OCH₃)₂.

Prior to the polymerization process, the catalysts can be precontactedwith small quantities of olefins (prepolymerization), thus improving theperformance of the catalysts and the morphology of the polymersprepolymerization is carried out maintaining the catalysts in suspensionin a hydrocarbon solvent (hexane or heptane, for example) andpolymerizing at a temperature from ambient to 60° C. for sufficient timeto produce quantities of polymer from 0.5 to 3 times the weight of thesolid catalyst component. It can also be carried out in liquidpropylene, at the temperature conditions indicated above, producingquantities of polymer that can reach up to 1000 g per g of catalystcomponent. In particular, even if many other combinations of thepreviously said catalyst components may allow to obtainpropylene-hexene-1 copolymer compositions according to the presentinvention, the copolymers are preferably prepared by using catalystscontaining a phthalate as inside donor and (cyclopentyl)₂Si(OCH₃)₂ asoutside donor.

Said propylene-hexene-1 copolymers are typically produced by awell-known polymerization process, such as in liquid (bulk or slurry) orin gas phase. According to the preferred polymerization process suchcopolymers are produced by a gas-phase polymerization process carriedout in at least two interconnected polymerization zones.

The process according to the preferred process is illustrated in EPapplication 782 587.

In detail, said process comprises feeding the monomers to saidpolymerization zones in the presence of catalyst under reactionconditions and collecting the polymer product from said polymerizationzones. In said process the growing polymer particles flow upward throughone (first) of said polymerization zones (riser) under fast fluidizationconditions, leave the riser and enter another (second) polymerizationzone (downcomer) through which they flow downward in a densified formunder the action of gravity, leave the downcomer and are reintroducedinto the riser, thus establishing a circulation of polymer between theriser and the downcomer.

In the downcomer high values of density of the solid are reached, whichapproach the bulk density of the polymer. A positive gain in pressurecan thus be obtained along the direction of flow, so that it becomespossible to reintroduce the polymer into the riser without the help ofspecial mechanical means. In this way, a “loop” circulation is set up,which is defined by the balance of pressures between the twopolymerization zones and by the head loss introduced into the system.

Generally, the condition of fast fluidization in the riser isestablished by feeding a gas mixture comprising the relevant monomers tosaid riser. It is preferable that the feeding of the gas mixture iseffected below the point of reintroduction of the polymer into saidriser by the use, where appropriate, of gas distributor means. Thevelocity of gas transport into the riser is higher than the transportvelocity under the operating conditions, preferably from 2 to 15 m/s.

Generally, the polymer and the gaseous mixture leaving the riser areconveyed to a solid/gas separation zone. The solid/gas separation can beeffected by using conventional separation means. From the separationzone, the polymer enters the downcomer. The gaseous mixture leaving theseparation zone is compressed, cooled and transferred, if appropriatewith the addition of make-up monomers and/or molecular weightregulators, to the riser. The transfer can be effected by means of arecycle line for the gaseous mixture.

The polymer circulating between the two polymerization zones can becontrolled by dosing the amount of polymer leaving the downcomer usingmeans suitable for controlling the flow of solids, such as mechanicalvalves.

The operating parameters, such as the temperature, are those that areusual in olefin polymerization process, for example between 50 to 120°C.

This first stage process can be carried out under operating pressures ofbetween 0.5 and 10 MPa, preferably between 1.5 to 6 MPa.

Advantageously, one or more inert gases are maintained in thepolymerization zones, in such quantities that the sum of the partialpressure of the inert gases is preferably between 5 and 80% of the totalpressure of the gases. The inert gas can be nitrogen or propane, forexample.

The various catalysts are fed into the riser at any point of said riser.However, they can also be fed at any point of the downcomer.

The stereoregularity of propylene polymer (B1) is of the isotactic type,as shown by high values of xylene insolubility. In particular, thepropylene polymer (B1) is preferably insoluble in xylene at ambienttemperature in an amount over 90 wt %, more preferably over 95 wt %.

The propylene polymer (B1) can be obtained by polymerizing the monomersin the presence of Ziegler-Natta catalysts as described above for thecomponent (A).

The ethylene copolymer (B2) can comprise a diene, conjugated or not,such as butadiene, 1,4-hexadiene, 1,5-hexadiene andethylidene-norbornene-1. The diene, when present, is typically in anamount of from 0.5 to 10 wt % with respect to the total weight of theethylene copolymer (B2). Said ethylene copolymer (B2) can be obtained bypolymerizing the monomers in the presence of Ziegler-Natta catalysts asdescribed above for the components (A) and (B1).

The polymeric composition of the present invention can be obtained byblending the components (A), (B1) and (B2) or by a sequentialpolymerization process. In the sequential polymerization process theorder of the polymerization stages is not a critical process feature,however it is preferred to prepare polymers with higher xyleneinsolubility, such as components (A) and (B1), before preparing theethylene copolymer (B2).

According to a preferred embodiment the composition of the presentinvention can be obtained by combining the component (A) with theheterophasic composition (B)

The process for preparing the heterophasic polyolefin composition (B) iscarried out by a sequential polymerization comprising at least twosequential steps, wherein components (B1) and (B2) are prepared inseparate subsequent steps, operating in each step, except the firststep, in the presence of the polymer formed and the catalyst used in thepreceding step. Preferably, the catalyst is added only in the firststep, however its activity is such that it is still active for all thesubsequent steps. Component (B1) is preferably prepared in a singlepolymerization stage.

The order of the polymerization stages is not a critical processfeature; however component (B1) is preferably prepared before component(B2). The polymerization can occur in liquid phase, gas phase orliquid-gas phase. For example, it is possible to carry out the propylenepolymerization stage using liquid propylene as diluent, and thefollowing copolymerization stage in gas phase, without intermediatestages except for the partial degassing of the propylene. Examples ofsuitable reactors are continuously operated stirred reactors, loopreactors, fluidized-bed reactors or horizontally or vertically stirredpowder bed reactors. Of course, the reaction can also be carried out ina plurality of reactors connected in series.

It is possible to carry out the polymerization in a cascade of stirredgas-phase reactors that are connected in series and in which thepulverulent reaction bed is kept in motion by means of a verticalstirrer. The reaction bed generally comprises the polymer that ispolymerised in the respective reactor.

Reaction time, pressure and temperature relative to the polymerizationsteps are not critical, however it is better if the temperature is from20 to 150° C., in particular from 50 to 100° C. The pressure can beatmospheric or higher.

The regulation of the molecular weight is carried out by using knownregulators, hydrogen in particular.

Alternatively, the heterophasic polyolefin composition (B) can beproduced by the gas-phase polymerization process carried out in at leasttwo interconnected polymerisation zones and described in detail above.

The polymeric composition of the invention can further comprise aninorganic filler agent in an amount ranging from 0.5 to 60 parts byweight with respect to 100 parts by weight of said polymericcomposition. Few examples of such filler agents are calcium carbonate,barium sulphate, titanium bioxide and talc. Talc and calcium carbonateare preferred. A number of filler agents can also have a nucleatingeffect, such as talc that is also a nucleating agent. The amount of anucleating agent is typically from 0.5 to 5 wt % with respect to thepolymer amount.

Pipe systems and sheets according to the present invention may be singlelayer or multilayer, wherein the layers can have the same or differentthickness. Typically the thickness of the sheets may vary between 0.25mm and 10 mm, preferably between 0.3 mm and 7 mm. In multilayer pipes,all the layers can be made from the same polyolefin composition.Otherwise, at least one layer is made from the polyolefin compositiondescribed above and the further layer(s) are made from amorphous orcrystalline polymers of R—CH═CH₂, where R radical is a hydrogen or aC₁-C₆ alkyl radical, or their mixtures, or fluorinated polymers, such aspolyvinyl difluoride. Examples of said polymers are isotactic or mainlyisotactic propylene homopolymers, polyethylene, polyolefin copolymers orfurther heterophasic polyolefin compositions.

Pipe systems and sheets according to the invention are produced inmanner known per se, such as by extrusion or injection moulding of thepolyolefin composition. Multilayer pipes are produced by coextrusion orother methods as well.

Extrusion of articles can be made with different type of extruders forpolyolefin, e.g. single or twin screw extruders.

With the polymeric composition according to the present invention it ispossible to achieve a material having high flexural modulus and at thesame time high creep resistance. This is due to the particularbalancement of the features of component A) such as the amount of1-hexene derived units, the polydispersity and the amount of thecomponent itself and the balancement of features of the heterophasiccomposition B) such as the amount of B1 and B2 used and the amount ofethylene units in component B2)

The following examples are given to illustrate the present inventionwithout limiting purpose.

The data relating to the pipe systems and sheets of the examples aredetermined by way of the methods reported below. Results of the testsare shown in Table 1.

Xylene Soluble Fraction: Determined as follows.

2.5 g of polymer and 250 ml of xylene are introduced in a glass flaskequipped with a refrigerator and a magnetical stirrer. The temperatureis raised in 30 minutes up to the boiling point of the solvent. The soobtained clear solution is then kept under reflux and stirring forfurther 30 minutes. The closed flask is then kept for 30 minutes in abath of ice and water and in thermostatic water bath at 25° C. for 30minutes as well. The so formed solid is filtered on quick filteringpaper. 100 ml of the filtered liquid is poured in a previously weighedaluminium container, which is heated on a heating plate under nitrogenflow, to remove the solvent by evaporation. The container is then keptin an oven at 80° C. under vacuum until constant weight is obtained. Theweight percentage of polymer soluble in xylene at room temperature isthen calculated.

Polydispersity Index: Determined at a temperature of 200° C. by using aparallel plates rheometer model RMS-800 marketed by RHEOMETRICS (USA),operating at an oscillation frequency which increases from 0.1 rad/secto 100 rad/sec. From the crossover modulus one can derive the P.I. byway of the equation:P.I.=10⁵ /G _(c)in which G_(c) is the crossover modulus defined as the value (expressedin Pa) at which G′=G″ wherein G′ is the storage modulus and G″ is theloss modulus.

Melt Flow Rate (MFR): According to ISO method 1133 (5 Kg, 230° C.)

Content of 1-hexene: Determined by I.R. spectroscopy

The infrared spectrum of a pressed film of the polymer is recorded inabsorbance vs. wavenumbers (cm⁻¹). The area of the combination bandbetween 4482 and 3950 cm⁻¹ is used for spectrometric normalization offilm thickness. A Partial Least Squares (PLS) calibration is applied tothe range 790-760 cm−1 in order to determine ethylene and hexene % byweight.

Content of ethylene: Determined by I.R. spectroscopy

The infrared spectrum of a pressed film of the polymer is recorded inabsorbance vs. wavenumbers (cm⁻¹). The area of the combination bandbetween 4482 and 3950 cm⁻¹ is used for spectrometric normalization offilm thickness. A Partial Least Squares (PLS) calibration is applied tothe range 790-760 cm−1 in order to determine ethylene and hexene % byweight.

Hydraulic Pressure Resistance: According to ISO method 1167-1, testswere carried out at temperature of 80° C. and under a circumferentialstress of 4.2 MPa.

Flexural elastic modulus: According to ISO method 178.

Component A

The component (A) was prepared according to the process disclosed inexample 1 of the patent application EP10150735.8, by varying the amountof 1-hexene added so that to obtain a copolymer of propylene andhexene-1 having a content of hexene-1 derived units of 0.4% by weight.The data of the copolymer are reported on table 1.

TABLE 1 Hexene-1 Content, wt % 0.4 Polidispersity Index 4.2Xylene-Soluble Content, wt % 1.3Component B)Preparation of the Solid Catalyst Component

Into a 500 mL four-necked round flask, purged with nitrogen, 250 ml ofTiCl₄ are introduced at 0° C. While stirring, 10.0 g of microspheroidalMgCl₂.1.8C₂H₅OH (prepared according to the method described in ex. 2 ofU.S. Pat. No. 4,399,054 but operating at 3000 rpm instead of 10000 rpm)and 9.1 mmol of diethyl 2,3-(diisopropyl)succinate are added. Thetemperature is raised to 100° C. and maintained for 120 min. Then, thestirring is discontinued, the solid product was allowed to settle andthe supernatant liquid is siphoned off. Then the following operationsare repeated twice: 250 ml of fresh TiCl₄ are added, the mixture isreacted at 120° C. for 60 min and the supernatant liquid is siphonedoff. The solid is washed six times with anhydrous hexane (6×100 mL) at60° C.

Polymerization

The catalyst system was formed by the catalyst component prepared asdescribed above, triethylaluminium (TEAL) as co-catalyst anddicyclopentyldimethoxysilane as external donor, with the weight ratiosindicated in the following Tables.

The propylene polymer compositions of the examples were prepared in atwo-step polymerization process, wherein the homopolymer A) was preparedin the first polymerization step by feeding the monomers and thecatalyst system into a gas-phase polymerization reactor comprising twointerconnected polymerization zones, a riser and a downcomer, asdescribed in the European Patent EP-A1-782587. The polymerizationmixture was discharged from said reactor, conveyed to a gas-solidseparator and the polymerized material was sent into a conventionalgas-phase fluidized-bed reactor where the copolymer B) was produced. Theoperative conditions are indicated in the Table 2.

The polymer particles exiting from the second polymerization step weresubjected to a steam treatment to remove the unreacted monomers anddried. The characteristics of the obtained polymer are reported on table3

TABLE 2 Component B 1 Component B1 TEAL/external donor wt/wt 4TEAL/catalyst wt/wt 5 Temperature ° C. 80 Pressure barg 27 Split holdupriser wt % 40 downcomer wt % 60 H2/C3 riser/downer mol/mol 0.003 Tm ° C.163 Component B2 Temperature ° C. 80 Pressure MPa 1.7 C2/C2 + C3 0.43H2/C2 0.009 C2 = ethylene; C3 = propylene; C6 = 1-hexene; H2 = hydrogen

TABLE 3 Component B Component B1 MFR (melt index) g/10′ 1.1Polydispersity 4.3 Xylene soluble % 1.8 Component B2 Ethylene content Wt% 51 Split % 10 Component B (total) Ethylene content Wt % 5.1 MFR g/10′1.1 Xylene soluble % 12 IV XS dl/g 4

Component A and component B have been added with the additives indicatedin table 4. in table 4 comparative example 1 is 100% component B example1 according to the invention is 5% of component A and 95% component Bwhile comparative example 2 is 10% of component A and 90% of componentB.

TABLE 4 Example Comp 1 1 Comp 2 Formulation DSTDP % 0.33 0.33 0.33 TALCO% 1.0 1.0 1.0 Component A % — 5 10 CA STEARATE - M % 0.05 0.05 0.05IRGAFOS 168 % 0.11 0.11 0.11 IRGANOX 1010 % 0.2 0.2 0.2 IRGANOX 1330 %0.11 0.11 0.11 Characterization MFR 5 Kg g/10′ 1.3 1.3 1.3 Index Yellownr. 2.7 2.7 3.3 XS % 9.3 8.9 8.7 Flexural Modulus 24 h MPa 1810 18501775 Flexural Modulus 7 Day MPa 1985 2030 1908 Tens. Str. @ break 24 hMPa 29.8 29.3 29.5 DBTT 24 h ° C. −33.7 −30.2 −20.7 ||Tm ° C. 163.9163.5 162.7

From table 4 it clearly results that the composition of example 1according to the invention shows a flexural modulus higher than thecomparative example 1 wherein component B is used and comparativeexample 2 wherein 10% of compound B is used. Furthermore Index yellow,and flexural modulus are increased.

Pipes of the material of example 1 and comparative example 1 wereobtained. Said extruded pipe has nominal diameter of 32 mm and wallthickness of 2.9 mm. Hydraulic pressure resistance at 80° C. and 4.2 MPaof said pipes were measured.

Comp example 1 Example 1 hydraulic pressure hours 497 2249 resistance

In table 5 it is shown that even by adding a small amount of componentA) the hydraulic pressure resistance is considerably increased.

The invention claimed is:
 1. A polyolefin composition comprising(percent by weight): A) from 1.0% to 9.5%; of a copolymer of propyleneand 1-hexene wherein said copolymer comprises from 0.1 to 5% ofrecurring units derived from 1-hexene; and B) from 80.5% to 99% of aheterophasic polypropylene composition comprising: B1) from 50% to 85%of a propylene homopolymer, said propylene polymer being insoluble inxylene at ambient temperature in an amount over 85% having apolydispersity Index ranging from 3 to 10; and a Melt Index from 0.5 to10 dg/min; and B2) from 5% to 50% of a copolymer of ethylene andpropylene having an ethylene derived units content ranging from 30% to70%; said polymeric composition having a Melt Index from 0.05 to 10dg/min.
 2. The polyolefin composition according to claim 1 having aFlexural Modulus higher than 1500 MPa.
 3. The polyolefin compositionaccording to claim 1 comprising (percent by weight): A) 2% to 8%, of thecopolymer of propylene and 1-hexene; and B) from 82% to 98%, of theheterophasic polypropylene.
 4. The polyolefin composition according toclaim 1 wherein the propylenen/hexane-1 component A contains from 0.3 to3% recurring units derived from hexene-1.
 5. The polyolefin compositionaccording to claim 1 wherein the heterophasic propylene compositioncomponent B comprises: B1) from 60% to 82% of the propylene homopolymerdescribed in claim 1; and B2) from 8% to 40% of a copolymer of ethyleneand propylene having an ethylene derived units content ranging from 40%to 60%.
 6. Pipe systems and sheets comprising a polyolefin compositionaccording to claim
 1. 7. Mono- or multilayer pipes and sheets wherein atleast one layer comprises the polyolefin composition according to claim1.